Step 1: Prepare Your Tenderloin. Remove the beef tenderloin from the refrigerator at least 1-2 hours before cooking to allow it to come to room temperature. Pat the tenderloin very dry with paper towels. Trim any silver skin and excess fat. If necessary, tuck the thinner tail end under and tie with kitchen twine to create a uniform cylinder.
Step 2: Season Generously. Rub the entire tenderloin with 1 tablespoon of olive oil. Season liberally and evenly with coarse salt and freshly ground black pepper. Press fresh rosemary and thyme sprigs onto the surface of the tenderloin.
Step 3: Sear for a Perfect Crust. Preheat a heavy-bottomed, oven-safe skillet (cast iron recommended) over medium-high heat until it’s smoking hot. Add the remaining 1 tablespoon of olive oil. Carefully place the seasoned tenderloin in the hot skillet. Sear on all sides, turning every 2-3 minutes, until a deep golden-brown crust forms all around (about 8-10 minutes total). Remove the skillet from the heat.
Step 4: Roast to Perfection. Add the unsalted butter to the skillet, along with any additional fresh herb sprigs. Baste the tenderloin with the melted butter and herbs. Transfer the skillet to a preheated oven at 400°F (200°C). Roast until your desired internal temperature is reached (120-125°F for rare, 125-130°F for medium-rare, 130-135°F for medium). This typically takes 20-35 minutes, depending on size and desired doneness. Use a meat thermometer.
Step 5: Rest and Serve. Once the tenderloin reaches your desired internal temperature, remove the skillet from the oven and transfer the tenderloin to a cutting board. Tent it loosely with foil and let it rest for at least 10-15 minutes. This allows the juices to redistribute, ensuring a tender and moist result. Remove the twine and slice the tenderloin into thick medallions against the grain. Serve immediately.